A major obstacle for the cost-effective production of renewable transportation fuels from lignocellulosic plant biomass is the difficulty of extracting sugars from the plant cell wall. Simple sugars are converted to fuel through degradation and saccharification of the obstinate plant cell walls and fermentation of these sugars to produce ethanol and other valuable products. Overcoming plant recalcitrance to releasing biomaterials bound in the cell wall is therefore an issue of primary importance in the development of biofuel technology.
Lignins, complex interlinking biopolymers derived from hydroxyphenylpropanoids, provide rigidity and structure to plant cell walls for plant growth and transport of water and nutrients, and are significant contributors to plant recalcitrance. Lignins are composed primarily of syringyl (S), guaiacyl (G) and p-hydroxyphenyl (H) monolignol subunits, which are derived from sinapyl, coniferyl and p-coumaryl alcohols, respectively. The subunit ratio and resulting structure of plant lignins varies according to the genotype, environment, tissue type and maturity of the plant and as such, lignins are very heterogeneous and can vary significantly between different plants, within different tissues of a single plant and even within a single plant cell (Simmons B A et al., Curr Opin Plant Biol. 13:313-20 (2010)). This complexity and heterogeneity hinders the development of conversion technology able to process a range of sustainable feedstocks in a cost-effective manner. Identification and manipulation of genes regulating cell wall biosynthesis and recalcitrance is one of the critical steps for overcoming such constraints related to efficient production of cellulosic sugars and ethanol using plant biomass.